Truss structures have many applications, such as solar arrays, enclosures, antennas, telescopes, solar sails and other structures in space or supports for bridges, piers, buildings or antennas, whether under water or on land. Metal and rigid composite components with mechanical deployment systems were used in the initial stages of the technology development to manufacture support structures for space applications. These structures were massive and could not be packed efficiently for transport. In space applications, for example, their lack of packing efficiency resulted in increased launch vehicle size and mass, which consequentially led to higher system launch costs.
The inherent disadvantages of rigid element mechanically deployed systems led to the development of structures fabricated from ultra-lightweight materials that also utilized mechanical deployment schemes. Although these systems achieved significant mass reductions from earlier rigid element designs, they also have the disadvantages of complex deployment systems, which make them susceptible to a number of failure modes in space, as well as low packaging efficiencies. Strain energy deployed systems were developed to eliminate the complexity of mechanical deployment systems by using the strain energy of the ultra-light weight material for deployment. However, strain energy deployed systems have the disadvantage of severe material and structural damage due to folding.
Taking advantage of the light loading conditions in space, inflatable structures have been used for the structural support of components such as antennas, solar sails, telescopes and solar arrays because of their high packing and structural efficiency and relatively simple deployment process. An example of an inflatable support structure is disclosed in U.S. Pat. No. 5,311,706 (Sallee). However, the components in these structures require highly precise manufacturing processes and the materials used for these components, i.e., polymer films and fabrics, sometimes result in structures having a high coefficient of thermal expansion. These systems also rely on continuous pressurization and regulation of the inflation system in order to maintain the stiffness required to support the space structure. A further disadvantage inherent in this apparatus is limited structural stiffness. Inflatable systems are also subject to puncture from orbital debris, permeation of the inflation gas through the gas retaining layer, and loss of gas due to manufacturing defects, such as seam or joint leaks, and therefore have a limited lifetime and require constant monitoring of performance.
Alternative methods to the inflatable structures is to use a structure which is both inflatable and rigidizable, such as shown in U.S. Pat. No. 5,579,609 (Sallee). The truss design consists of a series of discrete members connected together and overlain on an inflatable MYLAR or KAPTON bladder to form various shapes when the bladder is inflated. Within each of the discrete members are a series of Kevlar or glass fibers and a binder surrounding a heating wire or core. Upon activation of the wire or core, heat is given off which activates the binder which hardens the member. However, such a design has the disadvantage that a large electrical system is required to activate the cores and wires and each member of the structure must be electrically interconnected. Further, use of discrete members for the structure reduces the strength of the structure by placing stress on the joints of the structure.